How Too Much Fresh Water Can Hurt the Bay

After one of the wettest summers on record—Baltimore received more than two-and-a-half times the normal rainfall from June 1 to August 4 this year—we’re into hurricane season. And although Hurricane Florence may not be as bad for Maryland as originally predicted, it’s still expected to add to the state’s rainfall total.

That’s another surge of fresh water in a Chesapeake Bay that already is feeling the effects of all that rain.

Take oysters, natural filter feeders that help clean the water, for example. For year, advocates have been working to restore the bay’s once abundant oyster population. They’ve created oyster farms and sanctuary reefs, and in places like Harris Creek on the Eastern Shore, they’ve had some success.

But an especially rainy season can set the recovery back. Oysters need salt, and all this rain can dilute the water they live in. That’s often deadly for baby oysters. Adults can survive an influx of freshwater by clamming up for a while, but only for so long.

"If we have days and days of it like we have had and are expected to have in the future, that could even kill adult oysters," says Beth McGee, director of science for the Chesapeake Bay Foundation.

She says creatures that can’t move around, like oysters, are particularly vulnerable to changes in salinity.

But excessive rain also brings excessive pollutants. And that harms all Bay organisms. Sediment from construction sites and farm fields can smother underwater plants.

"A lot of critters rely on underwater grasses to hide," McGee says. "Crabs when they’re molting, larval fish, those kinds of things. So they’re really important ecologically so we’re hoping that they’ll be able to withstand what they’re seeing right now."

Those underwater plants also help add oxygen to the water.

Heavy rain also washes nitrogen and phosphorus from farm fields into rivers. In the city, pet waste and lawn fertilizers add to the nutrient load. These nutrients cause algae blooms, which suck up the oxygen aquatic organisms need to survive in the Bay.

And then there’s raw sewage often overflowing from Baltimore’s aging pipes into the streams.

Jenn Aiosa, head of the environmental nonprofit Bluewater Baltimore, says this summer has been noticeably worse than others for sewage overflows.

"We tend to see more when the system gets overwhelmed, when we get this volume of rain," she explains. "So, we have been taxing our stormwater and our sewage infrastructure in a way that’s been more dramatic than normal."

Abundant rain also brings with it a more visible pollutant: trash washing off the streets, down the storm drains, into the Jones Falls and into the Inner Harbor.

That’s where Mr. Trash Wheel, comes in. It’s one of three trash-collecting vehicles with conveyor belts that scoop steady streams of Styrofoam cups, cigarette butts, plastic bottles and who knows what else from the Inner Harbor and dump it all into a waiting dumpster.

Daniel Chase, a co-owner, says one big storm can wash enough trash into the harbor to fill 16 dumpsters. That’s "about the equivalent of about two standard size rowhouses, floor to ceiling, both stories."

And that’s only one river, one storm. The Bay has many tributaries and any trash not picked up by a trash wheel ends up in the Chesapeake, and eventually the Atlantic Ocean.

While Florence may be making landfall too far south to have a great effect on Maryland, McGee says it could still cause problems in the Bay.

"Hurricanes rotate in a counter-clockwise direction," she explains. "And what that does is the winds then can force water up into the Bay."

That’s what happened in 2003, with Hurricane Isabel. It struck North Carolina directly, but storm surges pushed water into the Chesapeake, flooding towns like Crisfield and Annapolis and creating erosion that added untold tons of sediment to the Bay.

It’s unclear whether that will happen again, but either way, rain is in the forecast for a long time to come. Scientists predict a warming climate will increase precipitation in the Chesapeake region, bringing more heavy downpours and surges of fresh water into the Bay.

Related Content

Last week, Governor Larry Hogan sharply criticized Pennsylvania and New York for not doing enough to slow pollution and trash flowing down the Susquehanna River into the Chesapeake Bay. Pennsylvania’s Secretary of Environmental Protection fired back, calling the remarks “careless and insensitive.”

But the two were a bit more conciliatory at Tuesday’s Chesapeake Executive Council meeting.

It’s known that oysters are not only a favorite delicacy, but also incredibly beneficial to their habitats because of their water-purifying powers. In fact, a typical adult oyster can purify up to 50 gallons of water a day.

But now, Maryland scientists wonder whether the bivalves can serve another purpose: to break up oxygen-starved “dead zones” plaguing the Chesapeake. And they’ve started an experiment in the Severn River, just north of the Route 50 bridge to test the idea.

Back in 2016, a team of scientists from the Virginia Institute of Marine Science said watermen lost an astounding number—145,000 crab pots, leading to the deaths of millions of dollars’ worth of crabs trapped in those pots.

But a different panel of scientists says it’s not as bad as they originally thought.